Beyond Blood Cancers
CAR-T’s Expanding Frontier
Victor Moreno, MD, PhD, Director of Clinical Research, START-Madrid-FJD
CAR-T cell therapy is entering a new era. After transforming outcomes in blood cancers, researchers are now tackling the tougher frontier of solid tumors. This article outlines the scientific and logistical challenges that have historically limited CAR-T’s reach, tumor heterogeneity, antigen selectivity, and complex manufacturing, and the innovations reshaping the field. It discusses advances such as universal “off-the-shelf” cells, faster on-site manufacturing, dual-target and logic-gated constructs, and cytokine-releasing “fourth generation” CAR-Ts. These advancements aim to overcome previous biological and logistical challenges, making cellular therapies a practical reality for patients with solid tumors.
CAR-T cell therapy has transformed treatment paradigms in hematologic oncology, reshaping clinical practice in B-cell malignancies by achieving durable remissions in patients with limited therapeutic options. Translation to solid tumors, however, has proven substantially more difficult.
Solid tumors present biological and logistical barriers that are fundamentally different from those in leukemia or lymphoma. Unlike B-cell malignancies—where a single, well-defined antigen such as CD19 can be targeted with limited off-tumor toxicity, solid tumors are more complex, genetically diverse, and physically shielded by their microenvironment. These differences have challenged scientists to rethink how CAR-Ts are designed, manufactured, and delivered.
Progress continues despite these challenges. In 2025, the FDA approved afamitresgene autoleucel, a MAGE-A4-directed T-cell receptor therapy for synovial sarcoma—the first engineered T-cell product approved for a solid tumor. While mechanistically distinct from CAR-T, the approval demonstrates that targeted cellular immunotherapies can meet regulatory endpoints in solid tumors. As researchers continue to refine cell engineering, antigen targeting, and production technologies, the next era of CAR-T therapy is beginning to take shape.
Understanding the Barriers in Solid Tumors
Translation of CAR-T therapy to solid tumors has required confronting fundamental biological differences. Unlike circulating malignancies, solid tumors contain heterogeneous cell populations with variable antigen expression, mutational profiles, and microenvironmental features. Identifying targets that are highly tumor-specific while sparing normal tissue remains challenging. Even partial antigen expression in healthy organs can trigger severe inflammatory toxicity.
A second obstacle is the tumor microenvironment itself. Solid tumors develop dense stromal barriers and secrete immunosuppressive cytokines that impede T-cell trafficking and function. The physical structure of the tumor limits immune-cell penetration, while inhibitory pathways—such as PD-1/PD-L1 and TGF-β signaling—further dampen T-cell activity. An extreme example of these challenges is pancreatic cancer: its fibrotic stroma and highly immunosuppressive milieu make it one of the most resistant targets for any immune-based approach.
These biological barriers have historically stalled CAR-T development in solid tumors, but they have also catalyzed new strategies in cell engineering. Current strategies include multi-antigen targeting constructs, integrated safety switches, and armored CARs that secrete immune-modulating cytokines locally. The 2025 approval of afamitresgene autoleucel for synovial sarcoma demonstrates that with appropriate target selection and engineering approaches, T-cell therapies can achieve clinical efficacy in solid tumors.
Engineering the Next Generation of CAR-T Cells
Overcoming the inherent barriers of solid tumors has required a wave of innovation in CAR-T design. Investigators are advancing beyond single-target constructs toward architectures that account for tumor heterogeneity and immune evasion. Dual-target CARs recognize two antigens simultaneously to reduce escape variants. Logic-gated circuits activate only in the presence of specific antigen combinations, improving selectivity and minimizing off-tumor toxicity.
Fourth-generation CAR-Ts, often referred to as TRUCKs (T cells Redirected for Universal Cytokine Killing), incorporate genes enabling local cytokine secretion within the tumor microenvironment that can recruit endogenous immune cells and counteract immunosuppression. Early-phase data from studies targeting Claudin 18.2 in gastric and gastroesophageal cancers, mesothelin in mesothelioma and ovarian tumors, and MAGE-A4 in several epithelial malignancies are beginning to show encouraging safety and activity profiles.
Combination approaches are also under investigation. Pairing CAR-T or TCR therapies with checkpoint inhibitors such as anti-PD-1 aims to mitigate T-cell exhaustion. Initial data suggest manageable safety profiles, though efficacy remains to be established. Bispecific antibodies represent a complementary strategy—redirecting endogenous T cells without ex vivo modification. While logistically simpler, these agents require continuous infusion over extended periods, unlike the single-administration model of CAR-T. Together, these advances signal a decisive shift toward more intelligent, adaptable, and durable cellular therapies for solid tumors.
The Manufacturing Challenge — From Lab to Patient
While engineering advances have addressed biological barriers, manufacturing remains a critical constraint for CAR-T deployment in solid tumors. The autologous workflow, encompassing leukapheresis, viral transduction, expansion, and quality control—typically requires two to three months from collection to reinfusion. This timeline often necessitates bridging therapy to maintain disease control during manufacturing.
To shorten these timelines, several technologies are converging. Automated, closed-loop manufacturing systems capable of on-site production are reducing process times from weeks to days. Using fresh rather than cryopreserved cells preserves viability and reduces expansion requirements. Some platforms have demonstrated the potential to deliver a complete CAR-T product within seven days, a step that could dramatically improve clinical practicality for rapidly progressing cancers.
Parallel progress is being made in allogeneic or “off the shelf” CAR-T products derived from healthy donors. These cells are genetically edited to prevent graft versus host disease and immune rejection, removing the need for patient-specific manufacturing. However, risks of immunogenicity and limited persistence remain open challenges. As these approaches advance, decentralised manufacturing capabilities and on-site automation may allow cellular therapies to be produced closer to the point of care, an essential advance for expanding access and accelerating treatment initiation.
Managing Toxicity
Safety remains the defining challenge for wider CAR T adoption. Toxicities such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) are well recognized in hematologic malignancies and remain areas of active management in solid tumor trials. These events arise from powerful immune activation, which—if unchecked—can lead to systemic inflammation and neurological symptoms.
Efforts to mitigate toxicity are evolving rapidly. Lower intensity lymphodepleting chemotherapy regimens are being tested to preserve T cell expansion while reducing collateral toxicity. Early or prophylactic use of IL 6 and IL 1 blockade has shown promise in minimizing CRS severity. Genetic control mechanisms, including engineered “safety switches” that can be triggered by small molecules such as antibiotics, offer clinicians the ability to deactivate infused cells if severe adverse events occur.
Clinical experience is also reshaping outcomes. As more centers gain hands on familiarity with CAR T protocols, toxicity recognition and management have improved markedly. Multidisciplinary teams of oncologists, neurologists, and critical care specialists now anticipate complications earlier, allowing most adverse effects to be reversed without long term impact. Ongoing research aims not only to enhance the safety profile of CAR T therapy but also to balance intensity and tolerability so that potential cures do not come at the expense of quality of life.
Making CAR-T Accessible
Access and cost will determine whether CAR T becomes a realistic treatment option beyond academic centers. Manufacturing complexity, prolonged inpatient stays, and stringent regulatory oversight contribute to high costs. Even in high income regions, the overall price of treatment can limit patient eligibility and strain healthcare budgets.
Academic and publicly funded centers have begun to explore lower cost production models that rely on shared infrastructure and streamlined workflows. In Spain, for instance, academic institutions have demonstrated the feasibility of manufacturing CAR T products at much lower costs, illustrating the role of publicly supported initiatives in improving accessibility. As automation advances and more treatment facilities gain the expertise to handle cellular therapies, the geographic reach of CAR T is expected to expand beyond major metropolitan hospitals.
Decentralised, on site production and broader clinician training will be key enablers of this transition. In the long term, competition among commercial, academic, and hybrid models should drive efficiency and cost reduction, mirroring the evolution seen with other complex biologics. Expanding accessibility will require not only technological advances but also coordinated policy and reimbursement frameworks to ensure that the promise of CAR T extends equitably to patients worldwide.
The Road Ahead—Progress & Promise
The future of CAR T therapy will depend on the convergence of biology, bioengineering, and systems innovation. Advances in antigen discovery, including surface proteomics or “surfaceome” profiling, are accelerating the identification of tumor specific targets that are both selective and widely expressed. These data driven methods may uncover new antigens that enable more precise targeting in solid tumors.
Clinically, combination regimens are being actively explored. Integrating CAR T with checkpoint inhibitors, cytokine modulators, or bispecific antibodies could enhance persistence and overcome resistance mechanisms, with efficacy signals still maturing. Lessons from hematologic oncology—particularly dual target and logic gated CAR designs—will continue to inform strategies for heterogeneous solid tumors.
Equally important will be refining delivery and accessibility. As technology and expertise spread, CAR T therapy could move gradually from a highly specialised procedure toward a more scalable clinical service if efficacy and safety continue to improve. Progress will also depend on practical advances in manufacturing speed, cost, and clinical experience. The path forward is one of integration: combining scientific ingenuity with practical frameworks that make cellular therapy a sustainable and more broadly accessible option for patients with solid tumors.
Author Bio
Victor Moreno, MD, PhD, is the Director of Clinical Research at START-Madrid-FJD and a medical professor at Universidad Autónoma de Madrid and CEU San Pablo. Part of The START Center for Cancer Research global network, START-Madrid-FJD is the largest Phase 1 clinical trials unit in Europe dedicated to oncology and hematology.
